COMBINING STRATIGRAPHY WITH HGM MODELS TO CHARACTERIZE WETLAND LANDFORMS FOR DELINEATION, DEVELOPMENT, AND REMEDIATION

Hydro-geomorphic models (HGM's) are tools being adopted for wetlands permitting, mitigation and banking. HGM's depend upon the identification of native plant populations occurring upon particular geomorphic surfaces having specific hydrologic conditions. These models require understanding of geomorphology, hydrology and soils; particularly if the area has been modified. Knowledge of local stratigraphic relationships improves the understanding of the wetland when working with HGM's since the outcropping of stratigraphic units controls the land form upon which wetland surfaces form. This study concentrates on pitcher plant flatwoods that occur in South Mississippi.

The study sites were limited to areas having reduced silt loams such as the Bibb or Trebloc soils, characterized by flat to nearly flat topography, and shallow ground water tables. The sites were divided between cleared areas and those areas that had naturally reverted to or been planted with pines. We found that all areas that were cleared for prolonged time periods contained higher numbers of pitcher plants and other rare plant species, while similar unmodified areas contained less biodiversity. Surface watertables are lowered by populations of pine trees which explains why canopied areas were less likely to be wet, but why did some cleared areas form wet pine flatwoods while seemingly identical cleared areas did not? The key to understanding this question turned out to be stratigraphic. Modified areas underlain by more permeable soils of the Citronelle Formation also have higher water tables than unmodified areas; but, these water levels generally are deeper than those of the Hattiesburg or Pascagoula formations and are less amenable to pitcher plants except where water tables are perched.

Wet pine flatwoods occur or with minimal excavation occur in cleared areas where Hattiesburg- equivalent Formations outcrop. This is an important tool for cost-effective mitigation. By utilizing wetland delineation maps, HGM's, and stratigraphic maps, a development plan that minimizes both wetland impact and development costs in terms of wetland permitting and mitigation can be accomplished.